In recent years, the MIMO (multiple-input and multiple-output) technique has been established and the MIMO technique has been used in many wireless communication standards. In order to practice the MIMO technique, a plurality of radio-frequency circuits are required. Accordingly, the circuit size or power consumption increases as the number of radio-frequency circuits is increased. Therefore, in order to suppress the increase cult size or power consumption, there arises a need to provide a time-division system that can perform processing for a plurality of branches (also referred to as streams) by time-division use of one radio-frequency circuit.
Patent Literature 1 and Patent Literature 2 each disclose a technique that time-divisionally uses an RF (radio frequency) circuit. Patent Literature 1 discloses an RF circuit for time-division receiver including a mixer. Also Patent Literature 2 discloses a technique for a direct sampling mixer (DSM).
It has been found that where a time-division receiver, which is represented by the above techniques, is used in a MIMO system, leakage between branches largely affects the reception characteristics of the MIMO system. Therefore, in order to prevent deterioration in reception characteristics, it is necessary to reduce leakage between branches in the time-division receiver as much as possible in the MIMO system. Leakage between branches refers to mixing of signals between the branches. Leakage between branches occurs where a time-divisionally used radio-frequency circuit includes an element having frequency response in a time-division receiver.
Frequency response is provided by parasitic capacitances. Therefore, ideally, if no parasitic capacitances are generated in the radio-frequency circuit, neither frequency response is provided nor leakage between the branches occurs.